Visual inspection device

ABSTRACT

A visual inspection device including a pinhole lens optically coupled to a sensor is provided. The pinhole lens has a pinhole placed at the distal end of the lens to capture the rays from an object to be inspected, a front optical group receiving the rays which cross the pinhole, and a rear optical group. The front optical group is configured to focus, on the rear optical group, the rays which cross the pinhole. The rear optical group is configured to focus, on the sensor, the rays received from the front optical group.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of co-pending U.S. patentapplication Ser. No. 16/943,699, filed on Jul. 30, 2020, which claimspriority to and benefit of Italian Patent Application No.202020000003196 filed Jun. 5, 2020, the entire contents of all of whichare incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to a visual inspection device forperforming quality control on objects.

In particular, the present invention relates to a visual device suitableto inspect hollow objects and capable of creating an image not only ofthe front surface of a cavity, but also of the side surfaces thereof,focusing them all simultaneously and without the need to enter thecavity.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a visual inspectiondevice capable of focusing, on the same sensor, the bottom and walls ofthe same cavity.

Another object of the present invention is to provide a visualinspection device having increased depths of field so as to inspectcavities having various sizes and shapes.

Such objects are achieved by a visual inspection device as described andclaimed herein.

The visual inspection device comprises a pinhole lens optically coupledto a sensor.

The pinhole lens has a pinhole placed at the distal end of the lens tocapture the rays from an object to be inspected, a front optical groupsuitable to receive the rays which cross the pinhole, and a rear opticalgroup.

The front optical group is configured to focus, on the rear opticalgroup, the rays which cross the pinhole. The rear optical group isconfigured to focus, on the sensor, the rays received from the frontoptical group.

In an embodiment, the pinhole has a diameter between 0.1 and 2 mm.

In an embodiment, the visual inspection device comprises elements foradjusting the distance between the rear optical group and the surface ofthe sensor for focusing the lens.

In a variant, the visual inspection device comprises a mechanical systemfor adjusting the distances between the front and rear optical groupsand the sensor for focusing the lens.

In a further variant, the visual inspection device comprises an adaptivelens inserted between the front optical group and the rear opticalgroup, in which the curvature of the adaptive lens is controllable tofocus the lens.

In an embodiment, the front optical group consists of refractiveelements alone.

In a variant, the front optical group consists of catadioptric elements.

In a further variant, the front optical group consists of reflectingmirrors alone.

In an embodiment, the front optical group comprises a primary mirrorconfigured to reflect, a first time, the rays passing through thepinhole, and a secondary mirror suitable to receive the rays reflectedby the primary mirror and convey them onto the rear optical group.

BRIEF DESCRIPTION OF THE FIGURES

The technical features of the invention according to the aforesaidobjects can be clearly found in the contents of the claims hereinbelowand the advantages thereof will become more apparent from the followingdetailed description, made with reference to the accompanying drawingswhich show one or more embodiments thereof merely given by way ofnon-limiting example, in which:

FIGS. 1 to 3 diagrammatically show the visual inspection deviceaccording to the present invention, in just as many embodiments;

FIG. 4 shows a visual inspection device according to the presentinvention, in the action of inspecting the cavity of an object;

FIG. 5 shows the image obtained from the inspection;

FIG. 6 shows another example of an object having a cavity to beinspected; and

FIGS. 7 and 7 a show two images of the object in FIG. 6 obtained withthe device according to the present invention, the second of which showsa defect in the side wall of the object.

DETAILED DESCRIPTION

A visual inspection device according to the present invention isindicated as a whole with 100 in the drawings. The visual inspectiondevice comprises a pinhole lens 20 optically coupled to a sensor 1.

The lens 20 is defined pinhole because it uses the pinhole principle,i.e. a small hole 4 (hereinafter called “pinhole”) capable of projectinglight.

While the hole, also known as “stop”, is positioned after the lenssystem in traditional lenses and performs the function of limiting theintensity of the light transmitted to the sensor, in the lens accordingto the present invention, the pinhole 4 is placed at the distal end ofthe lens 20, i.e. before the lens system, to project the rays capturedfrom the object to be inspected. By combining the pinhole 4 with theoptical power of a lens group as described hereinbelow, the lens 20 mayview not only a front surface of a cavity, but also the side ones, whilefocusing them all simultaneously.

The visual inspection device according to the present invention is nowdescribed in a first embodiment with reference to FIG. 1.

Lens 20 collects the rays from a concave object 5 with an acceptanceangle α. The rays are limited to passing through a pinhole 4 having amillimetric or smaller diameter. If the configuration shown in FIG. 1 isused, the opening range can vary from 0.1 mm to 2 mm in diameter.

In general, the size of pinhole 4 is affected by the actual focal lengthof the system and by the wavelength range in which the lens is to beused.

A front optical group 3 collects the rays from object 5 and focuses themon a rear optical group 2.

The rear optical group 2 focuses, on the sensor plane 1, the raysreceived from the front optical group 3.

In other words, the front optical group 3 serves to channel the raysfrom the side surfaces 52 and from the bottom 54 of the cavity 50 of theobject 5 to be observed. The rear optical group 2 serves to focus theimage generated on sensor 1.

Variations of the rear optical group 2 allow accommodating sensors 1having various sizes or various focusing methods. Thereby, the frontoptical group 3, formed by various lenses, can be left unaltered if adifferent sensor is used.

As shown in FIG. 5, the result of the optical work performed is a circleimage 30 in which image 54′ of the bottom 54 of a cavity 50 is in themiddle and image 52′ of the side surfaces 52 is continuously about theimage of the bottom. The outermost edge 56′ of the circle image 30 showsan edge 56 of the analyzed cavity.

The optical system can be configured to focus concave objects 5 havingvarious sizes. The optical system comprises not only holes with the sameproportions, but also with specific depth and diameter according to theuse. The lens 20 has a high depth of field; therefore, it is capable ofaccommodating cavities having various sizes, requiring a single initialfocusing operation.

The focusing procedure, i.e. the condition of possible increasedsharpness of object 5 on sensor 1 may be achieved by implementingvarious technical solutions, both optical and mechanical.

The focusing procedure may occur manually, by means of a variation ofthe distance between the rear optical group 2 and the sensor plane 1.

In a variant, focusing is obtainable by means of a mechanical systemwhich acts on the distances of the front and rear optical groups and thesensor 1.

In a further variant, focusing is obtainable by taking advantage of theoptical principles by inserting an adaptive lens 6 between the reargroup 2 and the front group 3.

In this latter case shown in FIG. 2, the optimal focus is adjusted bycontrolling the curvature of surface 7 of the adaptive lens 6. Thiscontrol may occur by applying a current in the system which encapsulatesthe adaptive lens 6 through an external electronic driver.

Focusing can be improved with this technical solution, withoutmechanically modifying the system. This strategy is useful if severaldifferent cavities are to be observed with the same lens. Despite thedepth of field of the system being quite high, improved results areobtained using focusing adjustments because the desired object can beput in the best focusing point.

The focusing procedure can be assisted via software by means ofartificial vision algorithms.

The mechanics connecting sensor 1 to lens 20 may include an adjustmentstep if a particular angle between the sensor and the generated imagewere required.

The front optical group 3 may consist of refractive elements (lensesalone), as in the embodiment in FIGS. 1 and 2, or of catadioptricelements (lenses and mirrors).

In the variant in FIG. 3, the primary refractive optical component ofthe front optical group 3 was replaced by two reflecting mirrors 9, 10which form a reflecting front optical group 8.

Instead of lenses, mirrors may be used when the cavity to be inspectedhas specific sizes, or sizes beyond the range of the depth of fieldallowed by the original system.

In this configuration, the light emitted by the hollow object 5 passesthrough the pinhole 4, then it is reflected a first time by a primarymirror 9 which conveys the rays onto a secondary mirror 10. It is a taskof the secondary mirror 10 to convey the light onto the rear opticalgroup 2, which projects the image onto sensor 1.

The same focusing methods provided for the device in FIGS. 1 and 2 arealso valid if a front catadioptric or reflecting element is used.Specifically, mechanical and optical adjustments can be obtained bymeans of adaptive lenses. A sensor phase adjustment may be performed.

The surfaces of the primary 9 and secondary 10 mirrors may be obtainednot only from flat or spherical surfaces, but also from surfacesrepresentable by polynomial (also called aspherical) functions in space.

The surface of sensor 1 can accommodate sensors of any size by varyingthe structure of the optical groups 3 and 2. For example, it is possibleto switch to sensors having a diagonal of ½″, ⅓″ and ⅔″ by changing afew lenses of the rear optical group 2.

By modifying the configuration of the rear optical group 3, sensorshaving larger sizes (such as 1″, 1.1″, 4/3″ or full frame) may be used.

The optics may be designed to work with the desired light spectrums.Specifically, it may be developed to work in the visible, ultravioletand in the three infrared spectrums SWIR, MWIR and LWIR. According tothe expected application, the wavelength of the captured light can varyby hundreds of nanometers (UV and visible) up to the tens of micrometers(LWIR limit).

The visual inspection device of the present invention is capable ofsimultaneously focusing, on the same sensor, the bottom and walls of thesame cavity. The image obtained does not need image stitching algorithmsbecause all the surfaces are continuously shown. Therefore, holes andcavities can be inspected while remaining outside thereof.

Moreover, the device according to the present invention has increaseddepths of field and can inspect cavities having various sizes withoutbeing changed. The minimum observable size is a hole of 5 mm in depthand 5 mm in diameter. There is no restriction on the maximum observablesize as the optics is capable of indefinitely focusing. The holes neednot be cylindrical, but their sizes have to remain within the allowedrange.

A typical operating setup is shown in FIG. 4. The working distancebetween the lens 20 and the object 5 varies according to the sizes ofthe cavity 50 to be inspected. The operating principle of the lensallows to view the interior of the object by simply remaining thereon,without the need to enter the cavity.

Image 30 obtained is projected onto sensor 1. The image shows both thebottom 54 and the side walls 52 of the object.

The visual inspection device according to the present invention isparticularly suitable in performing quality control of parts, as shownin FIGS. 6, 7 and 7 a. By being able to view both the bottom and theside surfaces of a hole, defects or imperfections can to be detectedwith a single image.

FIGS. 7 and 7 a show the image of two hollow objects 5. FIG. 7 is animage of a hollow object 5 with no defects. FIG. 7a is an image of anobject 5 in which there is a defect 58. It is worth noting how thedefect is clearly identified.

Moreover, the increased depth of field allows small- and large-sizedobjects to be inspected without further adjustments other than theinitial one. If the focusing operation is to be improved according tothe object used, mechanical adjustments or adaptive lenses can be used,as explained above.

The present invention, therefore, achieves its intended purposes,objects, and advantages.

Obviously, the practical embodiment thereof may also take differentshapes and configurations than that shown above without departing fromthe scope of protection as described and claimed herein.

Moreover, all the details may be replaced by technically equivalentelements, and any sizes, shapes and materials may be used according tothe needs.

What is claimed is:
 1. A visual inspection device, comprising a pinholelens optically coupled to a sensor, wherein the pinhole lens comprises:a pinhole placed at a distal end of the pinhole lens to capture raysfrom an object to be inspected; a front optical group suitable toreceive the rays which cross the pinhole; a rear optical group, whereinthe front optical group is configured to focus, on the rear opticalgroup, the rays which cross the pinhole, and wherein the rear opticalgroup is configured to focus, on the sensor, the rays received from thefront optical group the visual inspection device further comprising anadaptive lens inserted between the front optical group and the rearoptical group, a curvature of the adaptive lens being controllable tofocus the lens.
 2. The visual inspection device of claim 1, wherein thepinhole has a diameter between 0.1 and 2 mm.
 3. The visual inspectiondevice of claim 1, further comprising elements for adjusting a distancebetween the rear optical group and a surface of the sensor for focusingthe lens.
 4. The visual inspection device of claim 1, further comprisinga mechanical system for adjusting distances between the front and rearoptical groups and the sensor for focusing the lens.
 5. The visualinspection device of claim 1, wherein the front optical group comprisesrefractive elements.
 6. The visual inspection device of claim 1, whereinthe front optical group comprises reflecting mirrors alone.
 7. Thevisual inspection device of claim 6, wherein the front optical groupcomprises a primary minor configured to reflect, a first time, the rayspassing through the pinhole, and a secondary minor suitable to receivethe rays reflected by the primary mirror and convey them onto the rearoptical group.
 8. The visual inspection device of claim 1, wherein thesensor has a diagonal selected from: ½″, ⅓″, ⅔″, 1″, 1.1″, 4/4″, andfull frame.
 9. The visual inspection device of claim 1, wherein thefront optical group comprises catadioptric elements.
 10. The visualinspection device of claim 1, further comprising software configured toassist in focusing the lens.
 11. The visual inspection device of claim10, wherein the software comprises artificial vision algorithms.